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Mad Mike
Mad Mike, ASE Certified Technician
Category: Car
Satisfied Customers: 258
Experience:  20 years experience, all makes and models.
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4 oxygen sensors replaced on my 2005 Hummer SUT..stranded..500 miles

Customer Question

I had both catalyic convertors and 4 oxygen sensors replaced on my 2005 Hummer SUT after one of convertors plugged up and left me stranded 500 miles from home. My engine light is still on. I was told by 2 different mecahnics that it has to do with some filter or sensor that is tied to the transmission. Can you help?Customer
Submitted: 6 years ago.
Category: Car
Expert:  Mad Mike replied 6 years ago.

Hello, my name is XXXXX XXXXX welcome to JA.


Do you have the code that this set? If the mechanics didn't document the code, is there an autozone or similar parts store that may be able to get it for you?




Customer: replied 6 years ago.
Yes, they where. The dealer says because I bought after market parts is why my sensors are still going off. The codes are PO157,PO155,PO151,PO137 and PO131. I am at my wits end. I have noticed that there seems to be some problem with accleration.
Expert:  Mad Mike replied 6 years ago.

Because you used aftermarket parts...that's a good one. He should try standup...


Defective parts can cause problems, but it has nothing to do with the fact that they are aftermarket.


How many miles are on this?


Did those codes all come back after the Cats and O2 sensors, or were the codes not cleared out after those items were replaced?


If the codes were not cleared, you'll need to clear them out and then see which ones come back.



Customer: replied 6 years ago.
The codes where cleared but showed back up with 24 hours. The mileage at the time of the repacement was 82000...Onstar is telling me it is that there is a problem in the exhaust system...Is there maybe another sensor that could be causong this problem. The codes that the dealer gave me where-PO131,PO137,PO151,PO155 and PO157...
Expert:  Mad Mike replied 6 years ago.

What a bummer on the mileage. You missed warranty by 2000 miles. I could check your vein though, if you'd like me to see for sure.


Do you happen to know if these codes were also present before these items were replaced?


I suspect that there is a short to ground somewhere in the sensor power circuit. It is also possible that the O2 sensor fuses are blown, so be sure to check them in the underwood fuse block. The short could also be in one of the O2 sensors, but we'll see.


Do you have a 12v test light and a digital multimeter to continue? It would be nice to access a scan tool, but we may be able to get around that issue.


If you don't have either of these, I would suggest at least unplugging each O2 sensor to inspect the terminals. Make sure that none of the terminals have bent over pins or any visible damage. Give each wire a tug also, to see if the wires are damaged internally.

trace the engine harnesses also to look for anywhere that a metal bracket could have rubbed through the conduit and cut into the wires. sometimes wires even stick out of the conduit and get cut that way. Simply pull the harness away from anything suspicious and see if has cut into it. If you see damage, strip down the harness to access and repair the wires.


If these checks don't yield anything and you want to continue with the test light and multimeter, let me know and I'll provide the necessary info.




Customer: replied 6 years ago.
I have a 12v tester. Where would I locate the underwood fuse block?
Expert:  Mad Mike replied 6 years ago.

black box under hood on drivers side near fender. I see I had some typos there, sorry.


(underhood not Underwood) (VIN, not vein)